Observation of ordered arrays of adsorbed lysozyme by scanning tunneling microscopy

The lysozyme film formed on a Au(111) surface was observed at a molecular resolution by scanning tunneling microscopy (STM). The flat domains of this film was obtained by dipping the Au(111) surface into lysozyme solution (4μg/ml, pH = 4.5 and room temperature) for 4 h. We observed a clear image of the stripes formed by lysozyme molecules. Two types of ordered stripes were confirmed. One was a simple stripe with a gap of 4.6 nm, and the other was a paired stripe with the periodicity of the pair is 6.2 nm. The latter case could be explained with a periodic bond chain model of the (110) surface of a lysozyme crystal.